Inorganic particulate materials, for example an alkaline earth metal carbonate (e.g. calcium carbonate) or kaolin, are used widely in a number of applications. These include the production of mineral containing compositions which may be used in paper manufacture or paper coating. In paper products such fillers are typically added to replace a portion of other more expensive components of the paper product. Fillers may also be added with an aim of modifying the physical, mechanical, and/or optical requirements of paper products. Clearly, the greater the amount of filler that can be included, the greater potential for cost savings. However, the amount of filler added and the associated cost saving must be balanced against the physical, mechanical and optical requirements of the final paper product. Thus, there is a continuing need for the development of fillers for paper which can be used at a high loading level without adversely effecting the physical, mechanical and/or optical requirements of paper products. There is also a need for the development of methods for preparing such fillers economically.
The present invention seeks to provide alternative and/or improved fillers for paper products which may be incorporated in the paper product at relatively high loading levels whilst maintaining or even improving the physical, mechanical and/or optical properties of the paper product. The present invention also seeks to provide an economical method for preparing such fillers. As such, the present inventors have surprisingly found that a filler comprising microfibrillated cellulose and an inorganic particulate material can be prepared by economical methods and can be loaded in paper products at relatively high levels whilst maintaining or even improving the physical, mechanical and/or optical properties of the final paper product.
Further, the present invention seeks to address the problem of preparing microfibrillated cellulose economically on an industrial scale. Current methods of microfibrillating cellulosic material require relatively high amounts of energy owing in part to the relatively high viscosity of the starting material and the microfibrillated product, and a commercially viable process for preparing microfibrillated cellulose on an industrial scale has hitherto before proved elusive.